HK1120667B - Arrangement for the mechanical interfacing of a mems micromotor with a clock wheel and timepiece comprising this arrangement - Google Patents

Description

Micro-electromechanical system micro-motor and clock wheel mechanical interface structure and timepiece comprising same

Technical Field

The present invention relates to a construction for a mechanical interface of a micromotor with a wheel and a timepiece comprising such a construction.

The invention relates more particularly to the construction of a mechanical interface for a micro-motor of the MEMS type with a gear, wherein the micro-motor is produced in the upper layer of a plate made of crystalline or amorphous material and comprises at least one actuator driving the rotor in rotation.

Background

In silicon micro-actuators, one way to convert electrostatic energy into work is to arrange the structure as a "comb" formed by a movable finger and a fixed finger, respectively, and set at two different potentials. The movable fingers are attached to a comb, which is itself attached to a capsule guided linearly by springs. These actuators are produced by photolithography and dry plasma etching of a single crystal silicon layer typically 50 to over 200 microns thick.

In order to make the clock wheel rotate, it is necessary to convert the linear movement into a rotational movement, for example by means of a ratchet system in the case of the Accutron watch (USA) of Bulova, Mosaba of ETA, or by means of a hysteresis system, for example as described in document WO 2004/081695. Linear movement on silicon is on the order of tens of microns and ratchets driven by pawls must have teeth of equal size. To ensure reliable engagement, the positioning of the ratchet relative to the movable finger must be within tolerances well below the tens of microns mentioned above.

To create such a mechanical interface between the linear and rotary movement of the pawl actuator, document WO 2006/024651 proposes the use of a micro-actuator that drives a micro-fabricated wheel coaxial and integral with the clock pinion with very small teeth through the teeth in a hysteresis movement. This solution implies to adjust the micro-actuator with respect to the wheel for each assembly, since the radial positioning tolerance of one mechanism shaft of a sliding bearing, for example made of steel on ruby, is in the order of 40 microns. One solution may be to integrate a spring system on the MEMS to absorb the positioning gap, e.g. a bending mechanism of the ratchet, which is suggested in document WO 2006/97516. Positioning is thus ensured, but the detent or any other mechanism made of silicon therefore protrudes directly on the side of the chip, which makes handling during assembly more difficult and also makes it more directly exposed to dust.

Disclosure of Invention

The object of the present invention is to solve these problems by proposing a construction in which the microactuator drives a silicon rotor positioned on the same substrate as it. The object of the invention is to make the micromotor and the mechanism independent at the level of their radial play, while allowing pure torque to be transmitted from one to the other.

To this end, the invention proposes a construction of the type mentioned above, characterized in that a pinion coaxial with the rotor and arranged above the rotor is rotationally connected to the rotor by at least one pin received in a relative housing, and the pinion meshes with a gear.

According to other features of the invention:

the rotor comprises a plurality of shells angularly distributed in a regular manner around the rotation axis, and the pins are integral with the pinion;

the pin and the pinion are produced in a single piece;

each pin is received in the relative housing with a radial functional clearance and a circumferential functional clearance determined by design;

the upper layer of the plate comprises at least one bearing surface oriented towards the top, and the pinion is provided to abut against this surface when an axial force oriented towards the bottom is applied to the pinion;

the rotor is guided in rotation by a shaft mounted in the plate;

the rotor is guided in rotation by the same shaft as the pinion;

the pinion meshes with the wheel in a meshing zone located close to the outer peripheral edge of the plate;

the rotor is rotated by the actuator via the pawl, and the ratchet engagement zone is angularly offset with respect to the engagement zone.

The invention also proposes a timepiece comprising a configuration according to one of the aforementioned features for the mechanical interface of the wheels of the gear train of the timepiece with the micromotor of the timepiece.

Drawings

Other features and advantages of the invention will become clearer when the following detailed description is read with reference to the accompanying drawings, given by way of non-limiting example and in which:

figure 1 is a cross-sectional view therein schematically showing a timepiece produced according to the teachings of the present invention;

FIG. 2 is a perspective view, partially in section, showing the core of the timepiece of FIG. 1, equipped with a driving module comprising a MEMS micromotor;

FIG. 3 is a top view schematically illustrating the drive module of FIG. 2;

fig. 4 is an exploded perspective view showing the drive module of fig. 2 and a housing surrounding the drive module;

FIG. 5 is an enlarged view in axial section according to plane 5-5, schematically showing part of the drive module and illustrating the rotation assembly of the pinion and the rotor of the micromotor about the axis;

FIG. 6 is an axial section schematic view according to plane X' X illustrating the pinion being driven by the rotor through the pin;

FIG. 7 is a schematic top view illustrating the pinion being driven by the rotor through the pin;

FIG. 8 is a schematic view in axial section according to plane X' X, illustrating a variant of the assembly of the shaft with respect to the rotor;

FIG. 9 is a bottom view schematically illustrating a resilient securing structure provided in the plate for clamping and centering the shaft according to the assembly of FIG. 8;

fig. 10 is a plan view schematically showing a silicon wafer, and illustrates an example of the structure of a plurality of micro motors on the wafer.

Detailed Description

In fig. 1, a timepiece 10 is schematically represented, timepiece 10 comprising a watch fitted with a drive module 13 according to the teachings of the present invention, drive module 13 being arranged here inside a casing 12.

Timepiece 10 includes a watch case 14 enclosed by a crystal 16, a dial 18 and an analog display device here including hands 20. A pointer 20 is provided to be driven in rotation by the driving module 13 according to the invention through a gear train 22 comprising, for example, reduction means. The drive module 13 is powered by a battery 24. The case 12, the driving module 13, the gear train 22 and the battery 24 are here mounted on a plate 26 and together form a core 27 of the timepiece 10, this core 27 being fixed inside the watch case 14. Of course, the core 27 comprises other elements (not represented), in particular an electronic module comprising an integrated circuit, a time base comprising quartz, a printed circuit board, etc.

In fig. 2, parts of the core 27 of the timepiece 10 are shown, in particular the plate 26, the case 12 and the gear train 22 being mounted on the plate 26.

The drive module 13 is intended to engage with a timepiece wheel, termed herein as input wheel 28 of the gear train 22.

The various elements of the drive module 13 according to the invention are shown in more detail in figures 3 to 7.

The drive module 13 comprises a plate 30 made of crystalline or amorphous material, for example the plate 30 is made of silicon, the plate 30 comprising a lower layer forming a substrate 32 and an upper layer 34 in which a micro-motor 36 of the MEMS (micro-electro-mechanical system) type is etched. The micromotor 36 is formed here by two actuators 38, 40 which drive in rotation a rotor 42, the rotor 42 being etched into the upper layer 34.

Each actuator 38, 40 comprises a stylus 44, 46 movable in a direction a1, a2 parallel to the plane of the plate 30. Each contact pin 44, 46 is provided with a pawl 48, 50 at its free end, the pawls 48, 50 being provided to cooperate with ratchet teeth 52 provided on the outer peripheral edge of the rotor 42 to sequentially drive the rotor 42 in rotation.

Preferably, each stylus 44, 46 extends in a direction a1, a2 that cuts the associated actuator 38, 40 into two generally symmetrical parts. Preferably, the first actuator 38 includes an advancing pawl 48 and the second actuator 40 includes a pulling pawl 50.

Each actuator 38, 40 is an electrostatic type actuator with interdigital combs and is created within the silicon plate 30 by etching. The plate 30 is here a silicon-on-insulator (SOI) type plate and comprises a thick lower layer 32 of silicon substrate, an intermediate layer 54 of silicon oxide and an upper layer 34 made of silicon having a thickness less than that of the substrate 32.

The fixed part of each actuator 38, 40 comprises a power supply pad 56, 58 provided for electrical connection to the electronic module, and the movable part of each actuator 38, 40 comprises a contact pad 57, 59 which places these movable parts at a predetermined potential, here at zero volts.

A micromotor comprising an electrostatic actuator produced in a silicon plate is described and represented, for example, in document WO2004/081695, which is incorporated herein by reference. In this document, the motor is produced in the silicon layer by etching. The motor includes a toothed drive wheel and an actuating finger that cooperates with the teeth of the wheel to cause the wheel to rotate. Each actuating finger is displaceably integrated with a movable comb that is displaced relative to the fixed comb as a function of a voltage applied to the fixed comb.

An embodiment using the SOI plate is described with reference to fig. 7A to 7D in the above-mentioned document.

According to an advantageous embodiment, each actuator 38, 40 is associated with a passive pawl 49, 51, the ratchet land of the passive pawl 49, 51 being located between the engagement zone 70 and the ratchet land of the associated ratchet. These passive pawls 49, 51 are maintained resiliently in engagement with the rotor 42 to ensure accurate angular positioning, particularly during the drive phase when the other pawls 48, 50 are displaced.

According to the embodiment represented in fig. 3 to 7, the rotor 42 is guided by an integrated or interposed central sliding bearing 60, which is produced simultaneously with the pawls 48, 50 and has a diametral clearance of between 4 and 10 microns, the lower limit of approximation corresponding to a silicon layer thickness of 80 microns. The pawls 48, 50 will work well if they function in a tangential path that is significantly larger than this clearance, i.e. typically between 20 and 100 microns. This corresponds well to the range of possible routes guided by the contact pins 44, 46 by means of deflection springs (not shown).

The torque of the rotor 42 is transmitted to the pinion 62 through a system similar to a crank. A pinion gear 62 located directly above the rotor 42 is coaxial with the rotor 42 and is guided by a central shaft 64. The pinion gear 62 is provided with a pin 66 which engages in a slot 68 of the rotor 42. Running clearances j _ group, j _ rot, j _ pi are provided between the various elements of the rotor 42 and pinion 62, as represented in FIG. 7. The rotor 42 and the pinion 62 are thus angularly coupled but laterally independent: the play in the xy-plane is taken up by the bearing 60 for the rotor 42 and the shaft 64 for the pinion 62. The lateral reaction forces due to the load are therefore not absorbed by the bearing 60 at the level of the rotor 42, but by the shaft 64 guided by the pinion 62. Thus, the micro-fabricated element of the micromotor 36 is protected from the large forces exerted by the timepiece element in the event of, for example, an impact.

Pinion 62 is provided to mesh with input wheel 28 of mechanism 22 in a meshing zone 70 located adjacent an outer peripheral edge 72 of plate 30.

According to an advantageous feature, the rotor 42 is provided on the plate 30 to minimize the distance D between the teeth 52 of the rotor 42 and the outer peripheral edge 72 of the plate 30 corresponding to the meshing zone 70. Further, the outer diameter of the pinion gear 62 is slightly larger than the outer diameter of the rotor 42 to protrude relative to the plate 30 within the mesh zone 70.

To simplify the illustration of fig. 7, the rotor 42 is shown as including only four slots 68 and the pinion gear 62 includes only four pins 66. According to an advantageous embodiment, such as the one particularly illustrated in fig. 3 and 4, eight slots 68 and eight pins 66 are provided.

According to a preferred embodiment, the angular position of each pawl 48, 50 with the ratcheting region of the rotor 42 is angularly offset relative to the engagement region 70. The ratchet engagement zone of each pawl 48, 50 forms an angle β with the axis X' X. α represents the angle between the radius through the pin 66 that abuts the edge of its slot 68 in engagement and the axis X' X (fig. 7) at a given moment.

Judicious selection of all the parameters (α, β, j _ rot, j _ pi, j _ group) for a given radius of the circle of the pinion 62, rotor 42 and pin 66 will then contribute to the efficiency of the mechanical energy transfer from the rotor 42 to the pinion 62. Thus, for the particular case of the invention with β -45 degrees, if the clearance is well adjusted, the efficiency for a system with four pins is close to 85%, which improves the efficiency with respect to the case in which the rotor 42 and the pinion 62 are glued to each other. In fact, in the latter case, all loads at the level of the bearing 60 and vertically between the outer periphery of the rotor 42 and the substrate 32 will have the form of lateral silicon-to-silicon friction because of the pivoting torque. However, silicon is somewhat disadvantageous for silicon friction, with a dry static coefficient close to 0.4.

This transmission solution makes it possible to change again the diameter of the pinion 62 to adapt the torque and the speed of rotation according to the load. Furthermore, if the pinion 62 is large enough and protrudes beyond the peripheral edge 72 of the plate 30, the meshing by incision is found to be simplified and the drive module 13 can be assembled on the plate 26 of the timepiece 10 in a modular manner, i.e. without having to disassemble/reassemble the driven wheel 28.

According to a number of variants:

the rotor 42 is micro-fabricated in place and on the same substrate 32 as the actuators 38, 40 to ensure mating to the bearings 60 and to the pawls;

another variant consists in manufacturing the rotor 42 separately on the same wafer or on another wafer, this rotor 42 then being assembled on the plate 30 or on the stator. This allows, in the case in which the rotor is guided by the bearing 60, to reduce the radial clearance, if desired;

a family of variants is formed by the rotor 42 and/or the pinion 62, the rotor 42 and/or the pinion 62 being micro-manufactured by a method different from DRIE machining (laser cutting, EDM, LIGA, micro-injection, etc.) and then assembled to the stator on the plate 30;

another family of variants is formed by pins 66, the pins 66 being formed by a second level of lithography in the pinion 62 and/or in the rotor 42.

The drive module 13 according to the invention allows increased modularity for adapting to a load by allowing the use of pinions 62 of various diameters without modifying the rest of the module 13. Thus, increased modularity is also obtained for the assembly, since the mechanical interface for connection to the timepiece gear train 22 is already present due to the presence of the pinion 62 integrated into the drive module 13 and rotationally connected to the micromotor 36.

The pinion 62 may be produced in metal, for example brass, so that the pin 66 of the pin connection is also produced in metal. The pinion 62 may also be produced in one piece with the pin 66 by moulding in a plastic material. The creation of a pinion 62 in plastic material with a molded-on metal pin 66 is also contemplated.

According to the embodiment represented in particular in fig. 4 and 5, the axis of rotation of the pinion 62 is formed by a stepped shaft 64 made of profile-turned metal, this stepped shaft 64 being inserted in the plate 30 through a first hole 74 produced in the substrate 32, and the stepped shaft 64 being pushed into a second hole 76 produced in the plate 106 of the casing 12. In this embodiment, the radial forces exerted on the shaft 64 are absorbed by the plate 106.

The shaft 64 includes a lower end portion 78, the lower end portion 78 and the lower intermediate portion 80 defining a first shoulder surface 82, the shoulder surface 82 being oriented toward the top and axially abutting the underside of the plate 30. The diameter of the lower intermediate portion 80 is substantially equal to the diameter of the first bore 74, and the lower intermediate portion 80 extends into the bore 74. The shaft includes an upper intermediate portion 84, the diameter of the upper intermediate portion 84 being slightly smaller than the diameter of the lower intermediate adjacent portion 80 and the upper intermediate portion 84 extending into a bore 86 of the pinion gear 62 to guide the pinion gear in rotation. The upper intermediate portion 84 and the upper end portion 88 define a second shoulder surface 90, and a retaining ring 92 is maintained in axial abutment against the second shoulder surface 90, said retaining ring being pushed onto the upper end portion 88.

When the rotational guidance of the rotor 42 is produced by the bearing 60, the bearing 60 is produced in the same way as the first bore 74 in a photolithographic etching process, which determines the centering of the shaft 64 relative to the bearing 60, a very good centering of the shaft 64, the pinion 62, the bearing 60 and the rotor 42 being obtained.

Further, the underside of the pinion 62 includes a ledge 94 opposite the bearing 60, the ledge 94 preventing the pinion 62 from axially abutting the rotor 42, particularly in the case of pivoting, which avoids damage to the rotor 42.

Another advantageous embodiment is shown in fig. 8 and 9, in which the shaft 64 is mounted in the plate 30 in a press-fit manner by means of a resilient fixing structure 96 provided in the substrate 32 around the first hole 74. In this embodiment, the radial force exerted on the shaft 64 is absorbed by the substrate 32 and thus by the resilient securing structure 96.

The resilient securing structure 96 is here formed by a flexible sheet 98 lithographically formed in the rear face of the plate 30. For the upper layer 34, including the pawls 48, 50 and the rotor 42, the front lithography is likewise very accurately aligned and centered (with an error of less than 1 micron) with respect to the rear lithography, and the result is more accurate guidance and centering than if the shaft were produced in one piece with the plate 30, since the radial clearance can likewise be reduced to 1 micron.

Due to this precise alignment and this centering, the bearing 60 may be eliminated such that the rotor 42 is directly guided in rotation by the shaft 64. Thus, the shaft 64 may simultaneously guide the rotor 42 and the pinion gear 62 for rotation. Since the shaft 64 is produced by contour turning, which makes it possible to obtain very limited manufacturing tolerances, a very precise assembly is obtained, which ensures particularly reliable operation of the actuators 38, 40. The rotor 42 is then guided by the outer axial wall of the shaft 64.

The shaft 64 may finally be fixed in the plate 30 by complementary fixing means, for example by welding to the substrate 32 with a weld 99 shown in fig. 8 or even by gluing.

The problem of friction against the shaft 64 can be solved by depositing a thin solid layer on the outer axial wall of the shaft 64, which makes it possible to reduce the friction between the parts.

The elastic fixing structure 96 can be chosen in particular from the examples described and represented in document CH 695395, or from other structures that ensure a precise centering and clamping of the shaft 64 on the plate 30, such as for example structures formed by flexible tongues with free ends.

Advantageously, considering in particular fig. 3, the actuators 38, 40 together depict an angle of approximately ninety degrees, the bisector of which passes through the meshing zone 70 and through the axis of rotation Z' Z of the rotor 42, so that the drive module 13 has a general "V" shape defined by the outer contour of the plate 30, this contour being optimized.

The plate 30 comprises a central portion 100 carrying the rotor 42 and two lateral portions 102, 104. The outer contour of the plate 30 generally corresponds to the intersection of two rectangles orthogonal together and forming the two lateral portions 102, 104 with a transverse rectangle forming the central portion 100, the transverse rectangle depicting a forty-five degree angle relative to each of the two other rectangles. A major portion of the surface of each lateral portion 102, 104 is occupied by the actuator 38, 40, while a major portion of the surface of the central portion 100 is occupied by the rotor 42. The engagement zone 70 is provided proximate one of the peripheral edges 72 of the central portion 100.

Preferably, the zones 56, 57, 58, 59 are arranged on the central portion 100, on the opposite side to the meshing zone 70 with respect to the axis Z' Z of the rotor 42.

It can be seen that the "V" shape of the drive module 13 has the advantage of allowing to optimize the efficiency of the micromotor 36 with respect to the surface of the plate 30 used and the advantage of optimizing the surface of the crystalline or amorphous material used to produce the micromotor 36 and the drive module 13. Thus, when the plate 30 is produced from a silicon wafer 101, as schematically shown in fig. 10, the "V" shape allows the replication plate 30 to be staggered across the wafer surface to maximize the number of micromotors 36 obtained from a given silicon surface. In particular, according to the example represented in fig. 10, the plates 30 can be arranged on the wafer in parallel columns in a herringbone manner, with the two adjacent columns Cn, Cn +1 oriented in opposite directions. Furthermore, two adjacent plates 30 of two adjacent columns Cn, Cn +1 have their laterally adjacent portions 102 aligned.

Preferably, the angle depicted by the two actuators 38, 40 is between ninety degrees and one hundred forty degrees. The larger the angle, the more optimized the staggering of the plates 30 on the wafer 100, but the large angle requires the stylus 44, 46 of the actuators 38, 40 to be displaced relative to their respective axes of symmetry a1, a2, which affects the mechanical efficiency of the actuators 38, 40.

According to the embodiment shown in the figures, the case 12 containing the driving module 13 comprises a lower plate 106, the lower plate 106 being provided to be fixed to an element of the timepiece 10, here to the plate 12 of the core, and the plate 30 of the driving module 13 being mounted on the lower plate 106. The housing 12 comprises a protective cover 108, which protective cover 108 covers the drive module 13 fixed to the lower plate 106, here by means of screws 109, and which holds the drive module 13 against the lower plate 106.

The upper face of the lower plate 106 here comprises a hollow or housing 110, in which the plate 30 of the drive module 13 is received in a substantially complementary manner.

Cover 108 includes an opening notch 112 in one of its outer peripheral edges, and pinion 62 is received in this notch 112 when cover 108 is assembled to lower plate 106.

Advantageously, a printed circuit 114 is interposed between lower plate 106 and cover 108 to allow micromotor 36 to be electrically connected to the electronic module of timepiece 10 through its plates 56, 57, 58, 59.

According to an embodiment variant (not shown), the drive module 13 can be mounted directly on the plate 26, which makes it possible to dispense with the casing 12, in particular to minimize the number of components, to facilitate the assembly of the core 27 and to minimize the space requirements of the drive device. A protection element may be provided on the drive module 13 to protect its components.

Claims (11)

1. Device for the mechanical interface of a MEMS-type micromotor (36) with a gear (28), wherein the micromotor (36) is produced in the upper layer of a plate (30) made of crystalline or amorphous material and comprises at least one linear actuator (38, 40) driving in rotation a rotor (42), characterized in that: a pinion (62) coaxial with the rotor (42) and disposed above the rotor (42) is rotationally connected to the rotor (42) by at least one pin (66) received within an associated housing (68), and the pinion (62) is meshed with a gear (28), wherein running clearances are provided between various elements of the rotor (42) and the pinion (62) such that the rotor (42) and the pinion (62) are angularly coupled but laterally independent.

2. The apparatus of claim 1, wherein: the rotor (42) includes a plurality of housings (68) angularly distributed in a regular manner about the axis of rotation, and the pins (66) are integral with the pinion (62).

3. The apparatus of claim 1, wherein: the pin (66) is produced in one piece with the pinion (62).

4. The apparatus of claim 1, wherein: each pin (66) is received within an associated housing (68) with a radial functional clearance and a circumferential functional clearance determined by design.

5. The apparatus of claim 1, wherein: the upper layer (34) of the plate (30) comprises at least one bearing surface (60) oriented towards the top, and the pinion (62) is provided to abut against this surface (60) when an axial force oriented towards the bottom is applied to the pinion (62).

6. The apparatus of claim 1, wherein: the rotor (42) is guided in rotation by a shaft (64) mounted within the plate (30).

7. The apparatus of claim 6, wherein: the rotor (42) is guided to rotate by the same shaft (64) as the pinion (62).

8. The apparatus of claim 1, wherein: the pinion (62) engages the gear (28) in an engagement zone (70) located adjacent an outer peripheral edge (72) of the plate (30).

9. The apparatus of claim 8, wherein: the rotor (42) is driven in rotation by a linear actuator (38, 40) via pawls (48, 50), and the ratchet land is angularly offset relative to the mesh land (70).

10. The apparatus of claim 1, wherein: the housing (68) is formed by a groove (68).

11. Timepiece (10) comprising a device according to claim 1 for the mechanical interface of the gear (28) of the gear train (22) of the timepiece (10) with the micromotor (36) of the timepiece (10).